Project Number: 57
Description: Build the circuit shown. Set the meter (M6) to the 0.5mA setting. Blow hard on the fan or place it in a very strong wind (either outside or near an electric fan). The "windmill" charges the battery (B4) when the wind is blowing hard, and the meter measures the charging current. Push the press switch (S2) to turn on the yellow LED (D5).
Snappy: A problem with using wind to power a light is that the wind isn't always blowing when you need the light on. On the other hand, the wind is often blowing when you don't need the light on. So here you use the battery to store energy from the windmill when the wind is blowing, and then it runs the yellow LED when you need it on. This way the light is always available from clean, free wind power.